Investigation on Acoustic Versus Functional Characteristics of Porous Asphalt

The theoretical background, standards, and contract requirements of pavement friction courses involve functional (e.g., permeability) and acoustic (e.g., resistivity) characteristics. Unfortunately, their relationship is partly unknown and uncertain. This affects the comprehensiveness and soundness of the mix design of asphalt pavements. Based on the issues above, the goals of this study were confined into the following ones: 1) to investigate the relationship between acoustic and functional properties of porous asphalts; 2) to investigate, through one-layer (1L) and two-layer (2L) models, the effectiveness of the estimates of acoustic input data through mixture volumetric- and permeability-related characteristics. Volumetric and acoustic tests were performed and simulations were carried out. Equations and strategies to support a comprehensive approach were derived. Results demonstrate that even if the measured resistivity is very important, permeability-based estimates of resistivity well explain acoustic spectra. Furthermore, the distance between observed and estimated peaks of the absorption spectrum emerges as the best error function.

The Frequency Spectrum and Time Frequency Analysis of Different Violins Classification as Tools for Selecting a Good-Sounding Violin

This work evaluates four violins from three distinct manufacturers, notably Eurostring, Stentor, and Suzuki, using a scientific approach. Eurostring1 and Eurostring2 were the names given to the two Eurostring units. The purpose of this study is to identify elements in various violins that could be used as tools for selecting a pleasantsounding violin by having them classified by a professional violinist. The signal’s time varying frequency was evaluated using a frequency spectrum and a time frequency plane, and the combination of frequency spectrum and time frequency domain is utilised. PicoScope oscilloscopes and Adobe Audition version 3 were used to record the acoustic spectra in terms of time and frequency. The time frequency plane is identified, and time frequency analysis (TFA) is produced by Adobe Audition spectrograms. The sound was processed in order to generate Fast Fourier Transform analysis: Fourier spectra (using PicoScope) and spectrograms (using Adobe Audition). Fourier spectra identify the intensity of the fundamental frequency and the harmonic spectra of the overtone frequencies. The highest frequencies that can be read are up to and including the 9th overtone. All violins have a constant harmonic overtone pattern with an uneven acoustic spectrum pattern. Eurostring1 showed inconsistent signal in the string G with 6th and 7th overtone missing, whereas Eurostring2 lack of the 6th overtone. Among the string D, only Eurostring1 display an exponential decay for the overtone. All the string A except for Suzuki showed nice and significant peak of fundamental and overtone. Stentor displays up to the 5th overtone. Among the string E, Suzuki showed inconsistent harmonic peak intensity. TFA revealed that the fundamental frequency of string E for Eurostring1 was lower than the first overtone. Only Eurostring1 has an uneven decay for the overtone frequency, whereas Eurostring2 exhibits a large exponential decay for the overtone frequency.

Prediction of wind turbine blade trailing edge noise under various flow conditions for a passive damage detection system

Noise generated by turbulent boundary layer over the trailing edge of a wind turbine blade under various flow conditions is predicted and analyzed for structural health monitoring purposes. Wind turbine blade monitoring presents a challenge to wind farm operators, and an in-blade structural health monitoring system would significantly reduce O&M costs. Previous studies into structural health monitoring of blades have demonstrated the feasibility of designing a passive detection system based on monitoring the flow-generated acoustic spectra. A beneficial next step is identifying the robustness of such a system to wind turbine blades under different flow conditions. To examine this, a range of free stream air velocities from 5 m/s to 20 m/s and a range of rotor speeds from 5 rpm to 20 rpm are used in a reduced-order model of the flow-generated sound in the trailing edge turbulent boundary layer. The equivalent lumped acoustics sources are predicted based on the turbulent flow simulations, and acoustic spectra are calculated using acoustic ray tracing. Each case is evaluated based on the changes detected when damage is present. These results can be used to identify wind farms that would most benefit from this monitoring system to increase efficiency in deployment of turbines.

Prediction of aortic valve regurgitation after continuous-flow left ventricular assist device implantation using artificial intelligence trained on acoustic spectra

Significant aortic regurgitation (AR) is a common complication after continuous-flow left ventricular assist device (LVAD) implantation. Using machine-learning algorithms, this study was designed to examine valuable predictors obtained from LVAD sound and to provide models for identifying AR. During a 2-year follow-up period of 13 patients with Jarvik2000 LVAD, sound signals were serially obtained from the chest wall above the LVAD using an electronic stethoscope for 1 min at 40,000 Hz, and echocardiography was simultaneously performed to confirm the presence of AR. Among the 245 echocardiographic and acoustic data collected, we found 26 episodes of significant AR, which we categorized as “present”; the other 219 episodes were characterized as “none”. Wavelet (time–frequency) analysis was applied to the LVAD sound and 19 feature vectors of instantaneous spectral components were extracted. Important variables for predicting AR were searched using an iterative forward selection method. Seventy-five percent of 245 episodes were randomly assigned as training data and the remaining as test data. Supervised machine learning for predicting concomitant AR involved an ensemble classifier and tenfold stratified cross-validation. Of the 19 features, the most useful variables for predicting concomitant AR were the amplitude of the first harmonic, LVAD rotational speed during intermittent low speed (ILS), and the variation in the amplitude during normal rotation and ILS. The predictive accuracy and area under the curve were 91% and 0.73, respectively. Machine learning, trained on the time–frequency acoustic spectra, provides a novel modality for detecting concomitant AR during follow-up after LVAD.

Aerodynamic noise characteristics of the flow past a circular cylinder

The present study experimentally investigates the aerodynamic noise from the flow past a fixed circular cylinder. The cylinders considered for the study have the diameters (d) in the range of 6 to 25 mm while its span length (L) is constant, which is 300 mm. The free stream velocity is varied up to 50 m/s, and the corresponding Reynolds number (based on d) varies up to 8.3 104, thus maintaining the flow past the cylinder in the subcritical regime. The discrete narrowband frequency tones depicting the aeolian tones are noted in the spectra. The results showed that the aeolian tone frequency decreases with an increase in the cylinder diameter and ceases to exist beyond the diameter of 15 mm. The corresponding Strouhal number of these tones is found to be in the range of 0.18 to 0.21, which is in congruence with the vortex shedding frequency in the subcritical regime. The maximum overall sound pressure level for cylinders having tonal noise is higher by around 30 dB compared to the background noise. Directivity studies show that the noise level is higher along the perpendicular direction of the jet flow. A sixth power Mach number scaling of the acoustic spectra shows a good collapse of the acoustic tonal amplitude.

Kinetic and Activation Characteristics of Structure Rearrangement Processes in Ethoxylated Isononylphenol Derivates

The paper presents the calculation results of the kinetic and activation characteristics of fast and ultrafast structure rearrangement processes in liquid hydroxyethylated derivates of isononylphenol (ОНФn). Parameters were calculated using the relaxation theory of acoustic spectroscopy of liquids based on the analysis of the acoustic spectra of speed and sound absorption of the hydroxyethylated derivates of isononylphenol. The paper shows that two simple regions of acoustic dispersion can describe the acoustic spectra in the frequency range from 12 MHz to 2 GHz and the temperature range from 253 K to 323 K. The dispersion region data in the hydroxyethylated derivates of isononylphenol correspond to the interconnected reactions of OH ... O bonding and breaking in chain associates and spatially branched network structures. It is noted that the change in the spatial structure of liquid hydroxyethylated derivates of isononylphenol can be considered as a set of the large number of independent (for non-collective processes) and interconnected (for collective processes) local rearrangements of the liquid structure as a result of the thermal motion of molecules. The proposed molecular mechanism of acoustic relaxation and the kinetic model of fast and ultrafast structure rearrangement processes of the hydroxyethylated derivates of isononylphenol made it possible to explain the main experimental results and to calculate the kinetic and activation characteristics of the structure rearrangement processes of the hydroxyethylated derivates of isononylphenol. This model and the kinetic and activation parameters of the hydroxyethylated derivates of isononylphenol can find application in development of various technologies for using nonionic surfactants.

Coupled Fan–Stator Aerodynamic and Acoustic Response to Inflow Distortion

Turbofan rotor–stator aeromechanic and aeroacoustics modeling has been traditionally developed by considering separately the aerodynamic and acoustic response of the fan and the stator to inflow nonuniformities. The present paper develops a model for the coupled fan–stator response for a realistic 3D geometry. The coupling mechanism is assumed to be mainly carried by scattered waves bouncing back and forth between the fan and the stator. The relationship between sources and state elements at three regions (inlet (1), in-between fan and stator (2), and exit (3)) is derived in terms of a scattering matrix S. The model is applied to two fan configurations: (1) a fully subsonic fan and (2) a transonic tip speed fan. The scattering matrix terms, up to the 5th blade passing frequency (BPF), are calculated by using CAAT, an Euler-based code. Results show coupling adds about 6 dB to the sound power level (PWL) of the transonic fan configuration but has a small effect for the subsonic fan configuration. The analysis of the propagating modes shows that, for the transonic configuration, the inlet mode at 1BPF propagates in regions 2 and 3 but is cut off in region 1. This reinforces the coupling process by trapping the acoustic mode 1BPF in region 2. Although this trapped energy is mainly due to the 1BPF of the fan wake, the fan scatters this energy into higher order acoustic modes and thus produces redistribution toward higher frequency of the acoustic spectra. Finally, adding a liner in region 2 reduces the energy of 1BPF mode propagating upstream and impinging on the fan. This mitigates the effect of the fan–stator coupling.

Timbre as Harmony—Harmony as Timbre

While timbre is typically understood as a property of a single musical note or event, many contemporary musical practices depend on the combination of multiple events—each with their own pitch, dynamic, and sound color—into unified composites with their own emergent timbres. Such composites are essential for composers of spectral music such as Gérard Grisey and Tristan Murail, but also can be heard in works by composers from Arnold Schoenberg to James Tenney. Viewed from the perspective of music psychology, these composites are “chimeric” percepts, thwarting the usual parsing of sonic input into separate sources through auditory scene analysis. When timbre is redefined to include composite events, it overlaps significantly with the discipline of harmony; many musical effects—textural sound-masses, synthesized acoustic spectra, virtual ring modulation, etc.—blur the lines between timbre and harmony, opening up a hybrid space between the two domains.